Method for planarizing unevenness of the seabed

ABSTRACT

At a location where unevenness  1000  is present, the condition of a seabed  200  is investigated in advance to examine the respective numbers of large filter units  51  and small filter units  52  to be used, and the position where the large filter units  51  and the small filter units  52  are to be installed. Based on the investigation result, the small filter units  52  are installed on the bottom of the unevenness  1000.  The large filter units  51  are installed on the upper surface formed by the installed small filter units  52,  and are leveled so that the upper surface formed by the installed large filter units  51  becomes flush with the seabed  200.

RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.12/979,602 filed Dec. 28, 2010 which claims priority to EP 09180856.8,the entirety of which his incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to methods for planarizing unevenness ofthe seabed.

2. Description of the Background Art

The seabed has geographical features called “unevenness” which is anuneven surface. Referring to FIG. 16A, unevenness 1000 as used hereinrefers to a portion that is recessed with respect to the surroundingseabed 200. The seabed 200 is not flat at a location where theunevenness 1000 is present. Thus, it may not be possible to provide astructure at such a location on the seabed 200. A method that deals withthe unevenness is disclosed in, e.g., Japanese Patent Publication No.2006-322400 of unexamined applications. In Japanese Patent PublicationNo. 2006-322400 of unexamined applications, for installation of afoundation of an offshore wind power generation using a caisson,covering material units are positioned between a friction increasing matprovided on the lower surface of the foundation, and the surface of theseabed in order to deal with the unevenness and to increase frictionalresistance. The number of covering material unit is determinedcorresponding to distribution of the ground level of the seabed.

According to Japanese Patent Publication No. 2006-322400 of unexaminedapplications, the covering material units are positioned under thefoundation in the case of a structure in which the foundation has aplanar bottom surface like a caisson. That is, the covering materialunits are positioned under the structure.

However, the structure of Japanese Patent Publication No. 2006-322400 ofunexamined applications cannot be applied to, e.g., linear structuressuch as submarine cables. If the covering material units are positionedonly under the submarine cable, the submarine cable can move onto theunevenness where no covering units are positioned, due to the tidalcurrents and the like. In such a case, referring to FIG. 16B, asubmarine cable 20 is bent over the unevenness 1000, imposing aconsiderable strain on the submarine cable 20 at both ends 21 and 22 ofthe unevenness 1000. Thus, the submarine cable 20 can be damaged. Oneconventional possible solution to this problem is to repair theunevenness by dumping crushed stones with a tremie pipe or the like.However, the dumped crushed stones can be carried away by the influenceof the tidal currents, whereby the unevenness can be restored. Anotherconventional possible solution is to repair the unevenness by installinga wire cylinder, a large concrete block, or the like therein. However,the wire cylinder, the large concrete block, or the like do notcompletely fit in the unevenness, and the part of the wire cylinder, thelarge concrete block, or the like, which does not fit in the unevenness,serves as resistance to the tidal currents, causing an excess flow. Suchan excess flow causes a phenomenon called “scouring,” a phenomenon thatthe seabed is worn away and chipped off, near the part of the wirecylinder, the large concrete block, or the like serving as resistance.Thus, the unevenness can be restored.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a method forplanarizing unevenness of the seabed.

According to the present invention, a method for planarizing unevennesswhich is an uneven surface of a seabed includes the steps of: installinga plurality of bag-shaped filter units, each containing predeterminedblock objects, on the unevenness; and leveling the plurality ofinstalled filter units so that an upper surface formed by the pluralityof installed filter units becomes flush with the seabed.

Preferably, the step of installing the plurality of filter unitsincludes the step of locating a position where the filter units are tobe installed, by using a GPS.

According to the present invention, the plurality of bag-shaped filterunits, each containing predetermined block objects, are installed on theunevenness, and the plurality of installed filter units are leveled sothat the upper surface formed by the plurality of installed filter unitsbecomes flush with the seabed. Thus, the unevenness can be turned into asubstantially flat seabed.

Preferably, the filter units include a first filter unit having a firstsize and a second filter unit having a second size larger than the firstsize, and, the step of installing the plurality of filter units includesthe step of placing the second filter unit on the first filter unit.

Preferably, the filter units have a predetermined size and the step ofinstalling the plurality of filter units includes the step of placingcrushed stones on said unevenness before placing the filter units withthe predetermined size.

Preferably, the filter units have a predetermined outer size and includea first filter unit having a first block objects with a first size and asecond filter unit having a second block objects with a second sizelarger than the first size, and the step of installing said plurality offilter units includes the step of placing the second filter unit on thefirst filter unit.

Preferably, the step of installing the plurality of filter unitsincludes the step of placing crushed stones at the bottom of saidunevenness before placing a plurality of the filter units.

Preferably, the volume of the filter units is equal or smaller than thevolume of the unevenness.

Preferably, the filter unit includes a bag body and block objects, andwhen the filter unit is hung up, assuming that the height of the bagbody from the closed portion to the bottom is H1 and the height of aspace without the block objects is H2, the amount of block objectsobtained by (H2/H1)×100 is 25-80%.

Still preferably, the porosity of the knitted fabric of the bag body is45% to 90%.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view showing a wind power generation system, atower, and a foundation, to which a method for constructing a foundationfor a wind power generation system of the first embodiment is applied.

FIG. 2A is a schematic view showing a filter unit (FU), and FIG. 2B is aschematic view showing the state where the FU is installed on an unevensurface of the seabed.

FIG. 3A is a side view of piles showing how FUs are located among piles,FIG. 3B is a diagram viewed from III B-III-B in FIG. 3A, and FIG. 3C isa diagram viewed from III C-III C in FIG. 3A.

FIGS. 4A, 4B, 4C, 4D, 4E, and 4F are diagrams sequentially illustratingthe method for constructing a foundation for a wind power generationsystem.

FIG. 5 is a schematic view showing a tower, and a foundation, to whichanother method for constructing a foundation for a wind power generationsystem of the first embodiment is applied.

FIGS. 6A and 6B are schematic view showing an example in which FUs areinstalled for an existing foundation.

FIG. 7 is a schematic view showing a tower, and a foundation, to which amethod for constructing a foundation for a wind power generation systemof the second embodiment is applied.

FIGS. 8A, 8B, 8C, 8D, 8E, 8F, 8G, and 8H are diagrams sequentiallyillustrating the method for constructing a foundation for a wind powergeneration system of the second embodiment, and FIG. 8I is a diagramviewed from position VIII I-VIII I in FIG. 8E. FIGS. 8J and 8K arediagrams showing an example in which FUs are installed for an existingfoundation.

FIGS. 9A, 9B, and 9C are diagrams sequentially illustrating a method forprotecting a submarine cable for a wind power generation system, andFIG. 9D is a diagram viewed from IX D-IX D in FIG. 9C.

FIG. 10 is a view showing how a FU covers a cable.

FIG. 11A is a diagram showing an example in which a submarine cable isprotected by using a plurality of FUs, and FIG. 11B is a diagram viewedfrom XI B-XI B in FIG. 11A.

FIG. 12A is a diagram showing an example in which a submarine cable isprotected by using two FUs, and FIG. 12B is a diagram viewed fromposition XII B-XII B in FIG. 12A.

FIG. 13A is a diagram showing an example in which a submarine cable isprotected by using a plurality of FUs, and FIG. 13B is a diagram viewedfrom XIII B-XIII B in FIG. 13A.

FIGS. 14A, 14B, and 14C are diagrams sequentially illustrating a methodfor planarizing an uneven surface of the seabed.

FIG. 15 is a schematic diagram showing an example of planarization of aconvex uneven surface.

FIG. 16A is a cross-sectional view showing an uneven surface, and

FIG. 16B is a cross-sectional view showing an example in which asubmarine cable is installed on the uneven surface.

DESCRIPTION OF THE PREFERRED EMBODIMENTS (1) First Embodiment

An embodiment of the present invention will be described below withreference to the accompanying drawings. FIG. 1 is a schematic viewshowing a wind power generation system and a tower which are settled ona foundation to which a method for constructing the foundation for awind power generation system according to an embodiment of the presentinvention is applied. Note that the present embodiment is described withrespect to an example in which the wind power generation system and thetower are supported by the foundation having piles as a base. FIG. 1shows an offshore wind power generation system 10 for generatingelectrical power from offshore wind energy, a tower 11, a base slabportion 12 a, piles 12 b, a plurality of filter units (hereinafterreferred to as the “FUs”) 50, and a cable 20. The tower 11 holds theoffshore wind power generation system 10, and extends down to a levelnear a seabed 200 through a sea surface 100. The base slab portion 12 a,which is made of concrete, is fixed to the tower 11 by anchor bolts, andsupports the tower 11. Each pile 12 b, which is made of a steel pipe, isprovided so as to be supported by a predetermined ground, and fixes thebase slab portion 12 a on its upper end by anchor bolts to support thebase slab portion 12 a. The FUs 50 are installed between the seabed 200and the piles 12 b. The cable 20 is extended outward from the tower 11near the seabed 200 to transmit the electricity, generated by the windpower generation system 10, to a land-based system (not shown). Notethat the tower 11 extends to such a height that enables the wind powergeneration system 10 to efficiently receive offshore winds. Thepredetermined ground 300 in which the piles 12 b are fixed indicates alayer of the ground called a “bearing layer” in FIG. 1. The bearinglayer is strong enough to endure the load of the wind power generationsystem and the tower under various conditions such as meteorological andhydrographic conditions. That is, the piles 12 b are driven into theground until they reach the bearing layer, and the piles 12 b are fixedin the bearing layer. Note that the foundation in the present embodimentincludes the base slab portion 12 a and the piles 12 b.

The structure of the FU 50 used in the present embodiment will bedescribed below. FIG. 2A is a schematic view showing the state where theFU 50 is suspended by a crane of a work ship or the like, and FIG. 2B isa schematic view showing the state where the FU 50 is installed on anuneven seabed.

Referring to FIGS. 2A and 2B, a bag comprising a bag body 501 knittedwith synthetic fiber yarn in which a predetermined amount of blockobjects such as crushed stones are placed is called the FU. The FU 50containing the block objects 502 includes a suspension rope 503 thatallows the bag body 501 to be suspended by a crane or the like, and aconnection portion 504 provided at an end of the suspension rope 503,and connectable to the crane for suspending the bag body 501. The FU 50used herein has a diameter of approximately 2.5 m when installed on aflat ground and its weight is roughly 4 t. The synthetic fiber used forthe bag body 501 is, e.g., polyester. Thus, the bag body 501 does notrust in the sea water, has high resistance to acidic and alkaline water,and is less likely to corrode. Note that the synthetic fiber is notlimited to polyester, and may be nylon, polypropylene, polyethylene, orthe like. In addition, since a yarn of a FU is synthetic resin,endocrine disrupter and heavy metal will not solve out and no adverseeffect is brought about.

In the bag body 501, the longer side N of the mesh of the net is 50 mm,and the yarn diameter M is 10 mm. It is preferable that the yarndiameter M and the longer side N of the mesh have a relation of 3≦N/M≦20(unit to be mm). Under this relation, none of the block objects 502described below drop out of the mesh and the bag body 501 keeps itsstrength longer.

It is preferable that the predetermined amount of the block objects 502be determined so that the porosity of the knitted fabric becomes 45% to90%. This ensures formation of porous voids in the FU 50, therebyreducing the dragging force while the water currents at the seabed 200are flowing through the bag body 501. Thus, no flowing water pressure isapplied to the FU 50, preventing a phenomenon called “scouring,” aphenomenon that the seabed 200 is worn away. Although the porosityrelates also to the size of the block objects 502 placed in the bag body501, at the porosity of less than 45%, the flowing water pressure isapplied to the FU 50, causing scouring around the bag body 501. On theother hand, at the porosity of more than 90%, the retention of the blockobjects 502 is reduced.

It is preferable that the bag body 501 be formed by knitted fabric(e.g., a raschel net) having an elongation of 30% to 80%. This enablesthe flexibility to be ensured, and also enables the bag body 501 tofollow any shape at an installation position of the FU 50, and to bemaintained in a stable state for a long time after installation of theFU 50. That is, the FU 50 can be stably maintained at the installationposition for a long time, regardless of whether the installationlocation is flat or not.

The block objects 502 contained in the FU 50 preferably has its diameterto be 50-300 mm and specific gravity large enough to prevent the FU 50from being dragged when the FU 50 is installed on the seabed 200. Forexample, the block objects 502 are crushed stones having a grain size of100 mm and specific gravity of 2.65. Thus, the FU 50 has a weight heavyenough to be unsusceptible to buoyancy and water currents under the sea.Note that, the smaller the grain size of the block objects 502 is, themore the bag body 501 adapts to the shape of the installation location.It is preferable that the grain size of the block objects 502 beapproximately about two times the longer side N of the mesh.

Next, the predetermined amount of block objects 502 to be placed in thebag is to be explained. With reference to FIG. 2A showing a bag when itis hung up, assuming that the height of the bag 501 from the closedportion 505 to the bottom is H1 and the height of a space without blockobjects 502 is H2. The predetermined amount of block objects 502 in thebag 501 is an amount that the value obtained by (H2/H1)×100 ispreferably 25-80%. The reason is that when the value is less than 25%,it means that the block objects reach its closed portion 505 and theadaptability to the installation position is reduced and it becomesdifficult to place the bag close to the desired position. When the valueis more than 80%, the shape of the FU can be changed easily, lessstable, and light weight against its volume, it is possible that the FUcan be driven away by a tidal wave.

In addition, since the FU has a structure described above, when it islocated in the seabed, the meritorious effect is brought about thatpreferable environment can be provided for plants and fish in the sea.

Next, the explanation is made as to the size of the FU. In the followingexplanation, the FU whose weight is less than 4 t, the diameter when itis set is less than 2 m, and the volume is less than 2 m3 is referred toas “a small FU”, whereas the FU whose weight is 4-20 ton, the diameterwhen it is set is 2 m-5 m, and the volume is 2-13 m3 is referred to as“a large FU”. The material and the diameter of the yarn, the mesh sizeincluding the longer side of the mesh, the diameter and specific weightof the block objects are same for both the small and the large FUs.

The Table 1 below shows an example of the relation between the weight(size) of the individual FU and an effective flow rate of the tidalcurrents. Note that it is assumed in Table 1 that the same block objectswhose diameter is 50-300 mm and specific weight is 2.65 are placed ineach FU.

TABLE 1 Weight of FU (t) Effective Flow Rate of Tidal Currents (m/s) 2Roughly 4.7 or less 4 Roughly 5.3 or less 8 Roughly 5.9 or less 20Roughly 7.0 or less

As shown in Table 1, an appropriate type of FUs may be used according tothe flow rate of tidal currents. For example, FUs having a weight of 4 tare used when the flow rate of the tidal currents is 5.0 m/s at theposition where the FUs are to be installed. In addition, it is possibleto change the weight of the FU and the size of block objects dependingon the conditions of the performance at the position where FUs are set.As shown in Table 1, the larger the FU, the more effective to the flowrate of the tidal current, compared with the smaller FU.

In the following description, the FU 50 described above is used unlessotherwise specified.

Note that, although the factors, such as the size of the FU 50 itself,the material of the yarn, the thickness of the yarn, the grain size andthe specific weight of the block objects are specified in the above FU50, the present invention is not limited to the FU 50 specified by thesefactors. The FU 50 may be specified by various other factors.

Note that, for example, it is preferable that the FU used here is ascouring preventing material for an underwater structure disclosed inJapanese Patent No. 3,696,389.

A method for installing the FUs according to the present embodiment willbe described below. FIG. 3A is a schematic-diagram seen from sideshowing an example around the piles 12 b when FUs are set around thepile 12 b right before the base slab portion 12 a is installed. FIG. 3Bis a diagram viewed from III B-III B in FIG. 3A, and FIG. 3C is adiagram viewed from III C-III C in FIG. 3A. First, referring to FIG. 3A,the FUs 50 are installed between the seabed 200 and the piles 12 bsupporting the base slab portion at their upper ends. As shown by chaindouble-dashed line X in FIG. 3A, it is preferable that the FUs 50 beinstalled with no gap formed therebetween, until a flat surface isformed by the plurality of FUs 50 according to the height of the headsof the piles 12 b. This allows the bottom surface of the base slabportion to closely contact the piles 12 b and the FUs when the base slabportion is installed, whereby the piles 12 b, the base slab portion, andthe FUs 50 are integrated together. This can increase the strength as afoundation including the base slab portion and the base, and can reducethe influence of tidal currents, including scouring. That is, this canincrease the bearing force as a foundation for supporting the wind powergeneration system and the tower. Referring to FIG. 3B, a point O is theposition where the center of the base slab portion is located when thebase slab portion is installed on the piles 12 b. The distance from thepoint O to the outermost position of the circumference of each pile 12 blocated farthest from the point O is R meters (hereinafter “m”). Acircle P1 is a circle having its center located at the point O andhaving a radius of R m. In this case, it is preferable that thelowermost layer of the FUs 50 be provided in a range surrounded by acircle P2 having its center located at the point O and having a radiusof about (R+W) m (see FIG. 3C). When W is between 4 m and 15 m, theeffect that scouring is prevented and it is preferable that W=6 m. Thelarger the installation range of the FUs 50 is, the more the effects ofthe FUs 50 as described above are expected to be obtained. However, theeffects of the FUs 50 substantially level off when the installationrange of the FUs 50 exceeds the circle P2. Thus, from the standpoint ofconstruction such as the number of FUs 50 to be installed and the amountof construction work, and the standpoint of the effects such as theeffectiveness of the FUs 50, the installation range of the lowermostlayer of the FUs 50 is preferably in the range surrounded by the circleP2 having a radius of about (R+6) m about the point O. Referring to FIG.3C, it is preferable that, in a range S (a portion of the circle P2other than the circle P1), the FUs 50 in the lowermost layer be arrangedin two to five layers in the radial direction concentrically about thepoint O (FIGS. 3A and 3C show an example in which the FUs 50 arearranged in three layers in the radial direction). Arranging small FUsin a plurality of lines in the radial direction in the range S canimplement higher stability than arranging large FUs in a single layer inthe radial direction in the range S. Further, a group effect is providedby the plurality of FUs 50 when the FUs 50 form a group. The groupeffect is the effect that a FU that is directly influenced by the watercurrents is supported by other FUs around the FU and a plurality of FUsforming the group can stably remain at the set location. As a result, ameritorious effect of preventing scour and so on can last for a longtime. Contrary, arranging the FUs 50 in a single layer in the radialdirection provides no effect of suppressing a turbulent flow that iscaused when the tidal currents strike the foundation, and the foundationcan be influenced by an excess flow generated by the tower. On the otherhand, the above group effect levels off when the FUs 50 are arranged insix or more layers in the radial direction.

The larger the overall thickness of the FUs 50, that is, the number oflayers of the FUs 50 in the vertical direction, is, the higher effectsthe FUs 50 are expected to have. This is because increasing the overallthickness of the FUs 50 improves engagement between the plurality of FUs50. Thus, the plurality of FUs 50 closely contact each other, are fixedtogether with no gap formed therebetween and decrease possibility ofearth and sand being sucked out from the seabed surface. This increasesthe stability of the plurality of installed FUs 50, enabling theinfluence of the tidal currents including scouring to be reduced for along time. On the other hand, the effect of preventing scouringsubstantially levels off when the overall thickness is equal to three ormore layers. Thus, as described above, from the standpoint ofconstruction such as the number of FUs 50 to be installed and the amountof construction work, and the standpoint of the effects such as theeffectiveness of the FUs 50, it is preferable that the overall thicknessof the FUs 50 be equal to two to three layers.

In addition, usually, one sized FUs are used to implement thisembodiment, FUs whose sizes are different can be used. In this case,when FUs of different sizes are installed in two or more layers, it ispreferable that the smaller FUs are set at the lower position and thelarger FUs are at higher position. The reason for this installation isthat the smaller FUs follow unevenness of the seabed, engagement betweenthe installed FUs and the seabed. As a result, FUs 50 maintain in astable state for a long time after installation. Further, since the topsurface of set smaller FUs is smoother than that of the seabed, thelarge FUs are stably located on the small FUs. Thus, flow rate of thetidal current can be effectively reduced.

Further, installing the FUs 50 around the seabed 200 having the piles 12b driven therein increases the lateral pressure applied to theunderground part of each pile 12 b from the surrounding ground. Thus, agap is less likely to be formed between each pile 12 b, and the groundand the bearing layer which surround the underground part of the pile 12b. This can suppress a moment that is generated near the seabed 200 ineach pile 12 b. Further, since a plurality of FUs installed serves as apart of the foundation, the size of the foundation can be compact.

As described above, since the plurality of FUs 50 are installed betweenthe seabed 200 and each pile 12 b, a gap is less likely to be formedbetween each pile 12 b, and the ground and the bearing layer whichsurround the underground part of the pile 12 b. This can suppress amoment that is generated near the seabed 200 in the pile 12 b, and canprevent scouring that occurs around each pile 12 b. As a result, thebearing force and the durability of the foundation having the piles 12 bas a base can be improved.

A method for constructing a foundation for a wind power generationsystem according to the present embodiment will be described below.FIGS. 4A through 4F are diagrams sequentially illustrating constructionof the foundation for the wind power generation system. First, at alocation where the wind power generation system is to be installed, thecondition of the seabed 200 and the condition of the tidal currents nearthe seabed 200 are investigated in advance to examine the size of theFUs, the number of FUs 50 and the position where the FUs 50 are to beinstalled (FIG. 4A). Next, based on the investigation result, the piles12 b as a base of the foundation are provided so as to be supported bythe bearing layer (FIG. 4B). Then, as described above, a plurality ofFUs 50 are installed in close contact with each other between the seabed200 and each pile 12 b (FIG. 4C). At this time, a flat surface is formedby the plurality of FUs 50 according to the height of the heads of thepiles 12 b. Then, a formwork 12 e for the base slab portion 12 a isinstalled on the upper ends of the piles 12 b (FIG. 4D). At this time,the bottom surface of the formwork 12 e and the upper ends of the piles12 b are fixed to each other. Then, concrete is placed in the formwork12 e to form the base slab portion 12 a (FIG. 4E). Then, the tower 11 isfixed to the upper end of the base slab portion 12 a (FIG. 4F).

According to the above method, the piles 12 b are provided so as to besupported by the bearing layer, the plurality of FUs 50 are installedbetween the seabed 200 and each pile 12 b, and the base slab portion 12a is provided on the upper ends of the piles 12 b. This preventsscouring from occurring for a long time, since influence of the tidalcurrent is decreased around the foundation on the sea bed and protectthe seabed 200 near the piles 12 b. In addition, this increases thelateral pressure that is applied to the underground part of each pile 12b from the surrounding ground. Thus, a gap is less likely to be formedbetween each pile 12 b. As a result, both the bearing force and thedurability of the foundation are increased. Further, since a pluralityof FUs installed serves as a part of the foundation, the size of thefoundation can be compact In addition, since the net yarn of the FUs ismade of synthetic fiber and FUs are porous, endocrine disrupter andheavy metal will not solve out and it is possible to provide biotope forseaweeds and fish. Further, the foundation can be made compact, sincethe FUs work as a par of foundation.

Next, the alternate embodiment is described. In this embodiment, asshown FIG. 5, a space is provided between the upper portion of the FUsand the base slab portion 12 a. Since the other portion is the same asabove described embodiment, the explanation thereof will not bereiterated.

In this alternate embodiment, similar to the above described embodiment,it is possible to prevent scouring from occurring for a long time, sinceinfluence of the tidal current is decreased around the foundation on thesea bed 200 and to protect the seabed 200 near the piles 12 b. Inaddition, since the lateral pressure is increased that is applied to theunderground part of each pile 12 b from the surrounding ground, a gap isless likely to be formed between each pile 12 b.

Next, further alternate embodiment is described. In this embodiment theFUs are installed in a foundation of an existing wind power generationsystem. FIGS. 6A and 6B are diagrams showing this embodiment. FIG. 6Ashows an existing wind power generation system to which this embodimentis applied. As shown in FIG. 6A, space is formed between the foundation12 a, 12 b and the surrounding seabed 200. FIG. 6B shows a state where aplurality of FUs 50 are installed between the piles, serving as the baseof the foundation and the seabed 200. In this embodiment, similar to theabove embodiment, scouring can be prevented from occurring for a longtime, since influence of the tidal current is decreased around thefoundation on the sea bed and protect the seabed 200 near the piles 12b. In addition, this increases the lateral pressure that is applied tothe underground part of each pile 12 b from the surrounding ground.Thus, a gap is less likely to be formed between each pile 12 b. In thisembodiment, the FUs are installed around the deformed concave portion ofthe seabed which might be formed by scouring, for example. The presentinvention may be applied to the seabed which is not deformed.

In this alternate embodiment, the same meritorious effect is broughtabout as described above.

In the first embodiment, an example is described in which one type ofFUs are installed. However, the present invention is not limited tothis, and two kinds of FUs, one is a large FU and the other is a smallFU, may be used. In this case, large FUs and small FUs are installedoverlapped. In addition, when FUs are installed in three layers, atfirst small FUs are installed in one layer at the bottom, and then, twolayers of large FUs are installed on the small FUs as described above.Thus, in addition to the effect described in FIG. 3, effects areobtained that FUs remain stably longer period and rate of tidal currentcan be effectively reduced.

A plurality of FUs may be installed in which different kinds of blockobjects are placed. For example, at first a first FUs including blockobjects having small size, and then a second FUs including block objectshaving large size. Thus, the first FUs prevents earth and sand frombeing sucked out from the seabed surface, follow the unevenness of theseabed. Further, engagement between the plurality of FUs 50 are improvedand FUs remain stably for a long time due to the fact that the pluralityof FUs 50 closely contact each other and are fixed together with no gapformed therebetween. In addition, since the second FUs having largesized block objects faces the tidal current, FUs are located stably anddecrease current speed of the tidal current effectively.

In addition, since “the size of FUs ” has nothing to do with “the grainsize of the block object filled in the FUs”, a synergetic effect isbrought about by the large FUs including block objects having large sizecompared with the effect brought about by large FUs including smallsized block objects, and small FUs including large sized block objects.For example, the large FUs including large sized block objects morestably maintain themselves than the small FUs including large sizedblock objects and the large FUs including small sized block objects.

Note that the above embodiment is described with respect to an examplein which the base slab portion 12 a is formed by providing the formwork12 e for the base slab portion 12 a on the upper ends of the piles 12 b,and placing concrete into the formwork 12 e. However, the presentinvention is not limited to this, and a concrete base slab portion 12 a,which has been fabricated in advance, may be provided on the upper endsof the piles 12 b.

In addition, although the steel pile is used in this embodiment, theconcrete pile may be used.

(2) Second Embodiment

The second embodiment will be described below. In the second embodiment,a wind power generation system is supported by a foundation having acaisson as a base. FIG. 7 is a cross-sectional view showing a wind powergeneration system, a tower, and a foundation to which a method forconstructing a foundation for a wind power generation system accordingto the present embodiment is applied. FIG. 7 shows an offshore windpower generation system 10, a tower 11, a base slab portion 12 a, acaisson 12 c, a plurality of FUs 50, and a power transmission cable 20.The tower 11 retains the offshore wind power generation system 10, andextends down to a level near the seabed 200 through the sea surface 100.The base slab portion 12 a, which is made of concrete, is fixed to thetower 11 by anchor bolts, and supports the tower 11. The caisson 12 c,which is made of concrete, is fixed in the excavated seabed 200, andsupports the base slab portion 12 a on its upper end. The plurality ofFUs 50 are installed between the seabed 200 and the caisson 12 c. Thepower transmission cable 20 is extended outward from the tower 11 nearthe seabed 200 to transmit the electricity, generated by the wind powergeneration system 10, to a land-based ground system (not shown). Notethat the foundation in the present embodiment includes the base slabportion 12 a and the caisson 12 c, and the caisson 12 c is formed byplacing concrete into a formwork. The FUs 50 used in the presentembodiment are similar to those of the above embodiment.

A method for constructing a foundation for a wind power generationsystem according to the second embodiment will be described below. FIGS.8A through 8H are diagrams sequentially illustrating construction of thefoundation for the wind power generation system. FIG. 8I is a diagramviewed from position VIII I-VIII I in FIG. 8E. First, at a locationwhere the wind power generation system is to be installed, the conditionof the seabed 200 and the condition of the tidal currents near theseabed 200 are investigated in advance to examine the size and thenumber of FUs 50 and the position where the FUs 50 are to be installed(FIG. 8A). Next, based on the investigation result, the seabed 200 isexcavated to the depth at which the caisson 12 c, which is a base of thefoundation, is fixed by the seabed 200, thereby forming a hole 13 forinstalling the formwork 12 d for the caisson 12 c therein (FIG. 6B). Atthis time, an open cut method (open cut mining) may be used. The size ofthe drilled hole 13 is large enough to support the wind power generationsystem 10, the tower 11, the base slab 12 a and the caisson 12 c to beprovided therein. Then, a plurality of FUs 50 are installed flat on thebottom surface of the drilled hole 13 (FIG. 8C). At this time, it ispreferable that the small FUs are installed. By this, the small FUs 50follow unevenness of the seabed and gaps to be formed between aplurality of FUs can be made small. As a result, when the caisson 12 c,the base slab portion 12 a, and the like are installed above the FUs 50,a plurality of FUs, the caisson 12 c, the base slab portion 12 a canmaintain their locations stable. In addition, when a gap formed betweenFUs is large, the gap can be reduced by using large FUs or by using bothlarge FUs and small FUs. In addition, there is no limitation as to thenumber of layers of FUs to be stacked. The more the number of layers,the more effect is obtained that earth and sand are prevented from beingsucked out from the seabed surface and that the caisson 12 c and thebase slab portion 12 a can maintain their stable state.

Then, the formwork 12 d for forming the caisson 12 c is installed on theFUs 50 installed on the bottom surface of the hole 13 (FIG. 8D). Notethat the formwork 12 d can be regarded as a part of the caisson 12 cdescribed below. Then, a plurality of FUs 50 are installed in closecontact with each other so as to fill the gap between the seabed 200 andthe formwork 12 d for the caisson 12 c as a base, that is, between theformwork 12 d for the caisson 12 c and the drilled hole 13 (FIG. 8E). Atthis time, it is preferable that the FUs 50 in the lowermost layer bearranged in two to five columns in the radial direction in a range ofwidth L from the outer circumferential edge of the drilled hole 13 (aportion of a circle P4 other than a circle P3 in FIG. 8I). It ispreferable that L is approximately 6 m. It is also preferable to installthe plurality of FUs 50 so that the FUs 50 having an overall thicknessof three layers closely contact the circumference of the formwork 12 dfor the caisson 12 c. Then, concrete is placed into the formwork 12 d toform the caisson 12 c (FIG. 8F). Then, the bottom surface of a formworkfor the base slab portion 12 a is fixed to the upper end of the caisson12 c by anchor bolts, and concrete is placed into the formwork for thebase slab portion 12 a to form the base slab portion 12 a (FIG. 8G).Then, the tower 11 is fixed to the base slab portion 12 a (FIG. 8H).

According to the above method, the seabed 200 is first excavated so thatthe caisson 12 c can be supported therein. Then, the plurality of FUs 50are installed flat on the bottom surface of the drilled hole 13. Theformwork 12 d for the caisson 12 c is installed, and the plurality ofFUs 50 are installed between the seabed 200 and the formwork 12 d forthe caisson 12 c. Concrete is then placed into the formwork 12 d to formthe caisson 12 c, and the base slab portion 12 a is provided on theupper end of the caisson 12 c. Since influence of the tidal current isdecreased near the foundation on the seabed 200, scouring can besuppressed for a long time and the seabed 200 near the caisson 12 c canbe protected. As a result, the bearing force and the durability of thefoundation can be improved. Further, since installed FUs serve as a partof the foundation, the foundation can be compact. In addition, since thenet yarn of the FUs is made of synthetic fiber and FUs are porous,endocrine disrupter and heavy metal will not solve out and it ispossible to provide biotope for seaweeds and fish.

Next, an alternate embodiment is described. In this embodiment the FUsare installed in a foundation using the caisson of an existing windpower generation system. FIGS. 8J and 8K are diagrams showing thisembodiment. FIG. 8J shows an existing wind power generation system towhich this embodiment is applied. As shown in FIG. 8J, space is formedbetween the foundation 12 a, 12 c and the surrounding seabed 200. FIG.8K shows a state where a plurality of FUs 50 are installed between thecaisson 12 c, serving as the base of the foundation and the seabed 200.Since the other portion of constructing the foundation is the same asabove described embodiment, the explanation thereof will not bereiterated. In this embodiment, the FUs are installed around thedeformed concave portion of the seabed which might be formed byscouring, for example. The present invention may be applied to theseabed which is not deformed.

In this alternate embodiment, the same meritorious effect is broughtabout as described above.

Note that the above embodiment is described with respect to an examplein which the caisson 12 c is formed by placing concrete, and then, theformwork for forming the base slab portion is installed thereon.However, the present invention may use a formwork capable of formingboth the caisson and the base slab portion by placing concrete therein.

Note that the above embodiment is described with respect to an examplein which the caisson 12 c is formed by installing the formwork 12 d ontothe FUs installed on the bottom surface of the drilled hole 13, andplacing concrete into the installed formwork 12 d. However, the caisson12 c, which has been fabricated in advance, may be installed onto theFUs 50 installed on the bottom surface of the drilled hole 13.

Note that the above embodiment is described with respect to an examplein which one type of FUs are installed. However, the present inventionis not limited to this, and two kinds of FUs, one is a large FU and theother is a small FU, may be used. For example, in the case where it isnecessary to follow unevenness of the seabed, small FUs are preferablyused. On the other hand, when it is necessary to prevent reduce speed ofthe tidal current, large FUs are used. In addition, a plurality of FUsincluding different kinds of block objects depending on the conditionsrequired. Thus, the similar effect is brought about as described in thefirst embodiment.

(3)Third Embodiment

The third embodiment will be described below with respect to aninstallation method of the FUs. A method for protecting a submarinecable for a wind power generation system will be described in thepresent embodiment. FIGS. 9A through 9C are diagrams sequentiallyillustrating the method for protecting a submarine cable for a windpower generation system, FIG. 9D is a diagram viewed from line IXD-IXDin FIG. 9C and FIG. 10 is a diagram showing conditions when a FU isinstalled. Note that FUs 50 used in the present embodiment are similarto those of the above embodiment.

First, at a location where the submarine cable 20 is to be installed,the condition of the seabed 200 and the condition of the tidal currentsnear the seabed 200 are investigated in advance to examine the size andthe number of FUs 50 and the position where the FUs 50 are to beinstalled (FIG. 9A). Next, the submarine cable 20 is installed on theseabed 200 (FIG. 9B). Then, an FU 50 is installed so as to cover thesubmarine cable 20 installed on the seabed 200 (FIG. 9C).

At this time, with reference to FIG. 10, conditions required areexplained. FIG. 10 is a diagram showing the cross section perpendicularto the direction which the submarines cable elongates. Morespecifically, assuming the center point of the cable section is Q andits radius is r(m), the point above the cable which is located at thedistance D1 (m) from the top surface of the cable 20 is T1, the pointswhich is located at the distance D2 (m) from the side surface of thecable 20 are T2 and T3, and equal two lower angles formed by a isoscelestriangle made by points T1, T2 and T3 are θ. In addition, when blockobjects placed in the FUs are fallen from upper position to the ground,a conical shaped mountain is naturally formed by the block object. It isassumed that the angle is defined as φ formed by the inclined side ofthe mountain and the ground. It is preferable that the FU cover thehatched isosceles triangle shown in FIG. 10 in which D1≧0.5 m, D2≧1.0 m,and θ≧φ. At this time, normally φ is 45 degrees or less. It ispreferable that θ is 30 degrees or less. In FIG. 10, the dotted lineshows the cross section of the FU satisfying the above describedconditions.

Since the submarine cable is fully covered by the FU stably, thesubmarine cable 20 is fixed so as not to move by the influence of thetidal currents around it (see FIG. 9D), and can be protected from, e.g.,anchors of ships, rolling stones carried by the tidal currents, and thelike.

According to the above method, the FUs 50 are installed so as to coverthe submarine cable 20. Thus, the submarine cable 20 is fixed by theseabed 200 and the FUs 50, and can be prevented from moving by theinfluence of the tidal currents around it and the like. This can preventgeneration of friction between the seabed 200 and the submarine cable20, and can prevent scouring near the installed submarine cable 20 for along time. As a result, the submarine cable 20 can be protected for along time.

Note that the above embodiment is described with respect to an examplein which a submarine cable is newly installed. However, the FU 50 may beinstalled so as to cover an existing submarine cable.

Note that the above embodiment is described with respect to an examplein which one FU 50 is installed. However, it is more preferable toinstall a plurality of FUs 50. The use of the plurality of FUs 50increases the weight for fixing the submarine cable 20, enabling thesubmarine cable 20 to be fixed firmly. In addition, as described in thefirst embodiment, the group effect is obtained and the cable can befixed stably by installing a plurality of FUs.

Next, some of examples in which the submarine cable 20 is fixed by aplurality of FUs 50 will be described below. FIG. 11A shows an examplein which a plurality of FUs 50 are continuously arranged in line in thedirection in which the submarine cable 20 extends (hereinafter referredto as the “extending direction of the submarine cable 20”), and FIG. 11Bis a diagram viewed from XI B-XI B in FIG. 11A. FIG. 11A shows only apart of installed FUs. FIG. 12A shows an example in which two FUs 50 arearranged side by side with the submarine cable 20 interposedtherebetween, and FIG. 12B is a diagram viewed from position XII B-XII Bin FIG. 12A. Note that, in this case as well, a plurality of FUs 50 maybe continuously arranged in two lines along the extending direction ofthe submarine cable 20. FIG. 13A shows an example in which the submarinecable 20 is fixed by using a multiplicity of FUs 50, and FIG. 13B is adiagram viewed from position XIII B-XIII B in FIG. 13A. In any case, theFUs 50 are installed so as to cover the submarine cable 20, whereby thesubmarine cable 20 is fixed by the seabed 200 and the FUs 50, and can beprevented from moving by the influence of the tidal currents around it.This can prevent generation of friction between the seabed 200 and thesubmarine cable 20, and can also prevent scouring near the installedsubmarine cable 20 for a long time. As a result, the submarine cable 20can be protected for a long time. In the above embodiment, a pluralityof FUs are continuously arranged. It is possible to install continuallya plurality FUs in an extending direction of the submarine cable 20. Forexample, by installing continually a plurality FUs at the position wherethe cable 20 is likely to be moved by the tidal current, it is possibleto minimize quantity of work and amount of FUs to be used.

Note that, in the above embodiment, even if scouring occurs around theFUs 50 provided to protect the submarine cable 20, the FUs 50 follow thedeformed seabed 200, and thus, repairs can be made by, e.g., merelyproviding the FUs 50 over the recessed portion of the seabed 200 by theamount corresponding to the amount of the recess. Thus, repairs can beeasily made at low cost.

Note that it is preferable that the method for protecting a submarinecable for a wind power generation system according to the aboveembodiment be applied to the case where the water depth to the seabed200 is about 3 m or more.

Note that the above embodiment is described with respect to an examplein which a submarine cable is protected by covering the cable with FUs.At this point, the submarine cable includes ones of telephone lines, theoptical fibers and so on. This method can be applied to the cases wherethe submarine long objects such as long tubes and pipelines for the gas,the oil and so on.

(4) Fourth Embodiment

Next, the fourth embodiment will be described below with respect to theinstallation method of the FUs. In the fourth embodiment, a method forplanarizing an uneven surface of the seabed will be described in thisembodiment. Basically, one sized FUs are used to planarize unevensurfaces. In the following an embodiment is described wherein two kindsof FUs whose sizes are different.

FIGS. 14A through 14C are diagrams sequentially illustrating the methodfor planarizing an uneven surface of the seabed. The large FUs and thesmall FUs described in the first embodiment are used. It is hereinassumed that it has been determined based on the investigation thatthese FUs are suitable for planarization in this embodiment. The blockobjects placed in the large and small FUs are those having diameter of50-300 m and specific weight of 2.65. As to other points, there is nodifference between the large and small FUs.

First, the condition of an uneven surface 1000 of the seabed 200 isinvestigated in advance to examine the respective numbers of large FUs51 and small FUs 52 to be used, and the position where the large FUs 51and the small FUs 52 are to be installed (FIG. 14A). Then, based on theinvestigation result, the small FUs 52 are installed on the bottom ofthe recess of the uneven surface 1000 (FIG. 14B). At this time, it ispreferable to install the small FUs 52 so that the upper surface formedby the small FUs 52 becomes as flat as possible. Then, the large FUs 51are installed on the upper surface formed by the small FUs 52, and areleveled so that the upper surface formed by the small FUs 52 becomesflush with the seabed 200 (FIG. 14C). Based on the description of theabove embodiments, using a plurality of different types of FUs, such asthe large FUs 51 and the small FUs 52, improves engagement between theplurality of different types of FUs, and the plurality of differenttypes of FUs closely contact each other. Thus, the different types ofFUs are integrated firmly, increasing the stability of the large FUs 51and the small FUs 52 installed in the recess of the uneven surface 1000.Thus, the influence of the tidal currents can be reduced. Moreover, thelarge FUs 51 are installed so that the upper surface formed by the largeFUs 51 becomes as flush with the seabed 200 around the recess of theuneven surface 1000 as possible.

It is preferable to install the FUs in ascending order of weight. Inthis case, the large FUs 51 are installed on the upper surface formed bythe small FUs 52. Thus, the small FUs follow the bottom of the unevensurface 1000 and it is possible to make the upper surface of the smallFUs flat. In addition, by the large FUs installed on the flat small FUs,the whole FUs can be stable.

In this embodiment, since the small FUs are installed on the bottomsurface of the uneven surface 1000, the large FUs are installed on thesmall FUs and the top surface of the installed large FUs are leveled sothat the upper surface formed by the small FUs 52 becomes flush with theseabed 200. Thus, the large FUs 51 and the small FUs 52 engage with eachother, whereby a highly integrated, substantially flat seabed 200 havingno gap between the FUs can be formed. As a result, the uneven surfacecan be turned into a substantially flat, firm seabed.

Note that the above embodiment is described with respect to an examplein which the concave uneven surface is leveled. However, the presentinvention is not limited to this, and this method can be applied to anexample in which the convex uneven surface is leveled. FIG. 15 is adiagram showing this example. With reference to FIG. 15, in this method,at first, the small FUs 52 are installed around the convex unevensurface similar to the above embodiment. Then a large FUs 51 areinstalled on the small FUs 52. After the large FUs are installed, thetop surface of the installed large FUs are leveled so that the uppersurface formed by the small FUs 52 becomes flush with the seabed 200. Asa result, it is possible to planarize the convex uneven surface againstthe seabed.

Note that the above embodiment is described with respect to an examplein which two types of FUs, which are the large FUs 51 and the small FUs52. However, the present invention is not limited to this, and only onetype of FUs may be used. That is, the uneven surface 1000 may beplanarized by leveling one type of FUs so that the upper surface formedby the FUs becomes flush with the seabed 200. A plurality of types ofFUs, containing different types of block objects from each other, may beused to planarize the uneven surface 1000. For example, FUs containingblock objects having 100 mm diameter and FUs containing block objectshaving 200 mm diameter are used. In this case, FUs containing blockobjects having small diameter prevents earth and sand from being suckedout from the seabed surface and follow the unevenness of the seabed.Further, two kinds of FUs having different sized block objects, engagewith each other, and can be integrated with no gap therebetween. It ispreferable to install the FUs in ascending order of the grain size ofthe block objects. In this case, since the FUs with small grain sizefollow the shape of uneven surfaces 1000 and it is possible to form aflat surface on the upper surface of the small FUs and the whole FUs arestably installed since the large FUs are installed on the flat surfaceof the small FUs.

The method for planarizing the uneven surface of the seabed according tothe above embodiment may be applied together with, e.g., a barge vesselfor dumping crushed stones. In this case, the uneven surface 1000 of theseabed 200 may be planarized as follow. First, crushed stones are dumpedfrom the barge vessel to the bottom of the recess of the uneven surface.After a desired amount of crushed stones is dumped, the large FUs 51 andthe small FUs 51, for example, are installed as described in the aboveembodiment by using the method for planarizing the uneven surface of theseabed. This enables the uneven surface to be efficiently planarized atlow cost.

Note that the above embodiment is described with respect to an examplein which the uneven surface 1000 is planarized. After the uneven surfaceis planarized, a submarine cable for a wind power generation system maybe installed so as to extend on the planarized uneven surface, or anunderwater structure may be installed on the planarized uneven surface.As described in the above embodiment, the submarine cable may be fixedand protected by using the FUs.

Note that, in the above described first to fourth embodiments, theposition where the FUs 50 are to be installed may be located by a globalpositioning system (GPS). For example, a work ship for installing theFUs 50 on the seabed 200, and a tow body for submerging to investigatethe condition under the sea according to signals received from the workship are applied to the above embodiment. The tow body includes: abathymetric sonar for radiating sound waves in a fan-shaped radiationpattern to the seabed, and receiving reflected waves from the seabed tomeasure the depth to the seabed; an oscillation sensor for measuring andcorrecting the tilt of the bathymetric sonar associated with oscillationof the tow body; a water pressure sensor for measuring an accurate waterpressure to keep track of a change in water depth of the tow body; and atransponder for calculating the distance to the work ship and theazimuth of the tow body. The work ship includes: an operation apparatusfor operating the tow body; a GPS positioning apparatus for keepingtrack of the position of the work ship; and a GPS azimuth sensor forkeeping track of the azimuth of the work ship; an undersea positioningsystem for receiving sound waves from the transponder of the tow body,and measuring the position of the tow body; dedicated software foranalyzing data obtained from the tow body, based on the respectivepositions of the tow body and the work ship; and a tow winch connectedto the tow body and the cable, for controlling movement of the tow body.First, the operation apparatus in the work ship is operated to submergethe tow body under the sea. The submerged tow body obtains dataregarding the condition of the seabed by using the bathymetric sonar,while transmitting its own position and condition to the work ship bythe oscillation sensor, the water pressure sensor, and the transponder.The obtained data regarding the seabed is transmitted to the work shipto keep track of the condition of the seabed by the dedicated softwareof the work ship. The position where the FUs are to be installed islocated by the obtained data from the tow body, the GPS positioningapparatus, and the GPS azimuth sensor. This enables the FUs are to beaccurately installed at a desired position. For example, the positionwhere the FUs are to be installed may be located and recorded by the GPSpositioning apparatus in the investigation that is conducted in advance,and the FUs may be installed based on the recorded data.

Note that, in the above described first to fourth embodiments, the FUs50 may be installed by suspending each FU 50 by a crane or the like. Inthis case, the FUs 50 may be installed by automatically releasing theconnection portion 504 of each FU 50 from the crane when the FU 50 ismoved to a predetermined installation position. This reduces, e.g.,labor and danger of divers who give instructions and assist in workingon the seabed, in the operation of releasing each FU 50 from the crane.

Note that, in the above described first to fourth embodiments, theplurality of installed FUs may be connected by connection members suchas a rope, a chain, or the like. This enables the stability between theplurality of FUs 50 to be maintained for a long time, whereby thebearing force and durability of the foundation can further be improved.

Note that, in the above described first to fourth embodiments, the FUs50 may be installed one by one, or more than one FUs 50 may be installedsimultaneously.

Although the embodiments of the present invention have been describedwith reference to the drawings, the present invention is not limited tothe illustrated embodiments. Various modifications and variations can bemade to the illustrated embodiments within a scope that is the same as,or equivalent to, the present invention.

What is claimed is:
 1. A method for planarizing unevenness which is anuneven surface of a seabed when installing submarine cables, long tubesor pipelines, comprising the steps of: installing a plurality ofbag-shaped filter units, each containing predetermined block objects, onsaid unevenness; leveling said plurality of installed filter units sothat an upper surface formed by said plurality of installed filter unitsbecomes flush with said seabed; and, installing submarine cables, longtubes or pipelines on said flush seabed.
 2. The method according toclaim 1, wherein said step of installing said plurality of filter unitsincludes the step of locating a position where said filter units are tobe installed, by using a GPS.
 3. The method according to claim 1,wherein said filter units include a first filter unit having a firstsize and a second filter unit having a second size larger than saidfirst size, and; said step of installing said plurality of filter unitsincludes the step of placing said second filter unit on said firstfilter unit.
 4. The method according to claim 1, wherein said filterunits have a predetermined size and; said step of installing saidplurality of filter units includes the step of placing crushed stones onsaid unevenness before placing said filter units with the predeterminedsize.
 5. The method according to claim 1, wherein said filter units havea predetermined outer size and include a first filter unit having afirst block objects with a first size and a second filter unit having asecond block objects with a second size larger than said first size and;said step of installing said plurality of filter units includes the stepof placing said second filter unit on said first filter unit.
 6. Themethod according to claim 1, wherein said step of installing saidplurality of filter units includes the step of placing crushed stones atthe bottom of said unevenness before placing a plurality of said filterunits.
 7. The method according to claim 1, wherein the volume of saidfilter units is equal or smaller than the volume of said unevenness. 8.The method according to claim 1, wherein said filter unit includes a bagbody and block objects, and; when said filter unit is hung up, assumingthat the height of said bag body from the closed portion to the bottomis H1 and the height of a space without said block objects is H2, theamount of block objects obtained by (H2/H1)×100 is 25-80%.
 9. The methodaccording to claim 8, wherein the porosity of the knitted fabric of saidbag body is 45% to 90